With development of the display technique, most of widely used display device (e.g. display panel, display device and so on) utilizes a RGB (Red, Green, Blue) three color technique, and a RGB data for each of pixels may comprises numerical values for three R, G and B channels. In order to enhance displaying brightness, the RGB three color techniques are improved to generate a RGBW (Red, Green, Blue and White) four color technique. Many display devices are provided with a function of converting the RGB data into the RGBW data.
During a process of converting the RGB data into the RGBW data, a minimum value of the numerical values for the three R, G and B channels is selected, and a calculation is carried out based on a formula
      W    1    =            f      ⁡              (        x        )              =                  255        *            ⁢                        (                      x            255                    )                λ            (λ is a nonlinear conversion factor, which is normally taken as 2.5) to obtain a numerical value W1 for the W channel in the RGBW data; then, the numerical values for the three R, G and B channels are subtracted by W1 to obtain numerical values R1, G1 and B1 for the three R, G and B channels in the RGBW data so as to get the RGBW data; and finally, the RGBW data is utilized to display and output.
During the process of the present invention, the present inventor finds there are at least the following issues in the prior art.
On the basis of the converting process as mentioned above, a tone is not changed after each of the pixels are converted; however, since incorporation of the numerical value for the W channel, a saturation degree of the respective pixels after conversion are decreased at different levels. Since a chrominance is determined by combination of the tone and the saturation degree, there is a color difference at the respective pixels before and after conversion, so as to lead to a larger color difference before and after conversion.